Cannula system

ABSTRACT

A cannula system ( 1 ) comprising a tubular housing ( 7 ) having a front and a rear end. A slider ( 6 ) is displaceably mounted inside the housing ( 7 ) between a front and a rear limit position. A tear end ( 5 ) of a cannula ( 3 ) is rigidly joined to the slider ( 6 ), the front end of said cannula being fitted with a front end ( 4 ) having a tip to pierce biological tissue and extending into the front end of the housing ( 7 ) when the slider ( 6 ) is in the rear limit position. Means are provided to move the cannula ( 3 ) back. A catheter ( 2 ) is affixed to the rear end of the housing ( 7 ) in the direction opposite the direction of piercing and extends at least in part through the slider ( 6 ) and into the cannula ( 3 ), preferably as far as the front end of said cannula, when the slider ( 6 ) is in its front limit position and the cannula ( 3 ) projects from the front end of the housing ( 7 ). This cannula system offers the advantage that the catheter can be sealed at the tip and also may consist of several ducts without incurring any danger of leaks anywhere.

[0001] The invention relates to a cannula system of the species definedin the preamble of claim 1 and used to insert a catheter into biologicaltissue or the like.

[0002] A cannula system is known from the European patent document A20,567,321 with which to insert a catheter into biological tissue andwhich comprises a steel cannula with a sharp front tip and a rear endwhere the cannula is affixed to a plastic fitting. Moreover the knowncannula system comprises a plastic housing having a front aperture atits front end and a rear aperture at its rear end as seen in thedirection of piercing. The fitting is held against the housing betweenan advanced position wherein the front end of the cannula axiallyprojects beyond the housing, and a retracted position wherein thecannula is received in this housing and is displaceable in the axialcannular direction.

[0003] The known cannula system is used with a thin tube fitted withprojection enclosing the cannula and allowing detachably connecting thetube to the housing of the cannula system.

[0004] In order to introduce a catheter into biological tissue, forinstance the body of a patient using the cannula system, the cannulawill be in its advanced position wherein the sharp tip projects beyondthe housing and the front end of the tube in the direction of piercing,whereby it is possible then to insert the cannula into the skin of thepatient and to insert the thin tube into the patient's body through thepuncture.

[0005] After tube insertion, the user moves the fitting together withthe cannula into the retracted position wherein the cannula is receivedin the housing and separates the housing from the tube. The sole purposeof moving the cannula into its retracted position is to prevent contactwith the sharp cannula tip and hence any consequent injury andinfections.

[0006] Infusion may be immediately carried out through the tuberemaining in the patient's body or a flexible catheter may be insertedinto the patient's body to infuse liquids into this body or to removethem from it.

[0007] One drawback of the known cannula system is that following tubeinsertion, the cannula system must be detached from the tube before aflexible feed hose can be attached to the tube. This feature entailsfurther operational steps making handling more complex.

[0008] The PCT document US95/05,672 discloses a cannula system of thecited kind wherein the catheter is firmly affixed to the front end ofthe housing at which it terminates. In the retracted position of theslider, the cannula remains by its front end in the catheter and in thismanner sets up fluid communication between the catheter and the hollowinside of the slider, this slider being fitted at its rear end with ahose adapter.

[0009] This known cannula system incurs the drawback of mandatorilyrequiring open-tip catheters and precludes closed-tip catheters andmulti-duct catheters. Furthermore the system entails a large dead spaceand raises sealing difficulties.

[0010] The WO 95/20,991 patent document discloses a system for usingmicro-dialysis probes wherein the microdialysis probe first is seated ina cannula fitted with a longitudinal slot and this sub-assembly then ismade to pierce the tissue. Once the microdialysis catheter is present inthe tissue, the cannula is withdrawn and is separated through the slotfrom the fluid duct of the microdialysis catheter.

[0011] The patent document WO 96/25,088 discloses a device for usingsensors which also requires a slitted needle which, subsequent to sensorapplication, can be separated form the sensor.

[0012] Because of the slitted cannula, both known systems entail complexmanufacture and impractical operation.

[0013] The objective of the invention is to create a cannula system ofthe above cited kind which shall be suitable for closed-tip cathetersand for multi-duct catheters, for instance for microdialysis cathetersknown from the German patent document A1 197 14 572 or German patent 3341 170, and which shall be fully sealed.

[0014] The basic concept of the disclosure of the present invention isto guide the catheter through the slider and the housing as far as therear housing end and to affix the catheter in a direction opposite thedirection of puncturing, where the catheter can be directly connected tohoses. The catheter continues in especially advantageous manner beyondthe rear housing end. Sealing is assured everywhere.

[0015] The catheter being affixed to the housing and/or the slider onlyin the direction opposite that of puncturing, it cannot be accidentallypulled rearward out of the housing, while at the same time it ispossible to advance it in the direction of puncturing after suchpiercing arbitrarily far beyond the cannula tip. When the catheter isaffixed to tie slider in the direction of puncturing, the cannula may beleft prior to use in its retracted position wherein its tip isprotected. The slider will be advanced prior to use and the catheterwill be driven along.

[0016] However the catheter also may be wholly rigidly joined to therear housing end, in which case it runs as far as the cannula tip whenthis cannula is in its advanced position.

[0017] While it is basically possible to keep the slider manually inposition relative to the housing as the cannula is inserted, anappropriate embodiment of the invention makes use of locking means tolock the slider to the housing at least in the advanced slider position.Piercing may then be implemented solely by holding the housing.Thereafter unlocking, ie disengagement may be implemented and the slidermay be retracted. For that purpose one embodiment of the inventionprovides means for manually retracting the cannula. Advantageously thehousing comprises a slot running in the direction of displacement of thecannula and crossed by a radial protrusion of the slider. The slider canforced back by means of the said externally accessible protrusion.

[0018] In one embodiment of the invention, the slider comprises atwo-arm lever pivoting about an axis transversely to its slidingdirection, the front lever arm in the front limit position of the sliderengaging from behind an edge at the front end of the housing and thislever being disengaged, that is unlocked, by pressing on the front leverarm. Accordingly the two-arm lever is an actuator both to disengage andlock and to displace the slider.

[0019] A spring is provided in an especially appropriate embodiment ofthe invention to load the slider in the direction of its rear limitposition, the slider being kept in its front limit position by anexternally disengageable catch. In this embodiment the spring implementsthe return motion of the slider and cannula, thus facilitating handling.

[0020] When using a spring, the catch appropriately comprises a hookwhich is connected to the slider and which in the front limit positionof the slider engages behind an edge at the front end of the housing andwhich is yielding in the disengaging direction. This basic design of thecatch allows a further development in which the hook is fitted with aprotrusion projecting beyond the front housing end in such manner thatupon the cannula puncturing by the cannula, the protrusion hits thetissue surface and unlocks the hook. In this embodiment cannularetraction practically is automatic and no particular attention need bepaid to disengagement and retraction.

[0021] The disengaging means may be designed in a number of ways and theminimum distance between an obstacle and that housing which when reachedshall cause the disengaging means to unlock can be selected within widelimits. In an appropriate further development of the inventioncomprising the locking means, these are fitted with a locking bladeconnected to the adapter and which in the locking position elasticallyenters a radial clearance inside the housing, the disengaging meanscomprising an axially displaceable disengaging element of which thefront end projects radially beyond the front end of the housing and ofwhich the rear end comprises a disengaging blade extending inside thehousing and upon axial displacement of the disengaging element engagesunderneath the locking blade in the direction of the housing and movesout of the clearance. This design allows simple and economicalmanufacture and operates reliable.

[0022] In a further development of the above embodiment, the disengagingblade and the locking blade when at rest abut each other by means ofbevels in such manner that upon axial displacement of the disengagingelement the disengaging blade lifts the locking blade toward thehousing. This design offers simple and economical manufacture.

[0023] In a further development of the embodiment comprising adisengaging blade and a locking blade, at least two disengaging bladesand associated locking blades are present at diametrically oppositesites of the disengaging element or slider relative to the cannula. Thisembodiment prevents the disengaging element is prevented from being bentand the reliability of the disengaging means is improved.

[0024] In a further development of the embodiment comprising thedisengaging element, its front end is substantially annular. In thismanner reliable disengagement upon impact by the disengaging element onan obstacle is assured regardless of the angular position of the housingabout the cannula axis.

[0025] In another embodiment of the invention, the spring is helical, inparticular it is a compression spring coaxial with the cannula, and ismounted between the housing and the adapter. This embodiment isparticular simple and economical in manufacture. By appropriatelydimensioning the compression spring, the force acting on the slidertoward the retracted position after disengagement will be selectable.

[0026] Another embodiment comprises retention means to hold the housingagainst a body surface, for instance the skin of a human. In thisembodiment, following inserting the cannula cannula and moving it intoits retracted position, the cannula system is held for instance on theskin of a human in such manner that stressing the catheter by the weightof remnant cannula system on the catheter shall be prevented.

[0027] In a further development of the embodiment comprising retentionmeans, these adapters are fitted on the housing outside using adhesivemeans, in particular an adhesive strip. In this embodiment the housingadheres to the skin and can be subsequently removed from it, forinstance as the catheter is removed from the patient's body.

[0028] Appropriately the housing comprises a substantially flattenedsurface to rest on the body surface, for instance the skin of a human.In this design the housing rests in substantially two-dimensional manneron the skin and as a result pressure points or the like are precludedfrom the skin.

[0029] Lastly in another embodiment of the invention, the front apertureof the housing comprises a free inside width substantially correspondingto the outside diameter of the cannula. In this embodiment the cannulais laterally guided into its advanced position on one hand, wherebysideways slippage of the cannula is averted during puncturing. On theother hand when the cannula has been retracted, the catheter will beguided in the front aperture of the cannula system. This design avertsdamages that might arise when a flexible catheter is bent immediatelybehind the cannula tip and away from latter and thereby would rest byits outside surface against the cannula tip.

[0030] The invention is elucidated below by illustrative embodimentsshown in the drawings.

[0031]FIG. 1 shows a partly sectional sideview of a first embodiment ofthe cannula system of the invention in its advanced position,

[0032]FIG. 2 is a topview of FIG. 1,

[0033]FIG. 3 corresponds to FIG. 1, however the cannula being in itsretracted position,

[0034]FIG. 4 is a topview of FIG. 3 on the cannula system of FIG. 3,

[0035]FIG. 5 is an enlarged section V-V of FIG. 1,

[0036] FIGS. 6-9 elucidate the use of the cannula system or FIGS. 1-5,

[0037]FIG. 10 is a sideview of a second illustrative embodiment of thecannula system of the invention, the cannula being in its advancedposition,

[0038]FIG. 11 shows the cannula system of FIG. 10, with the cannula inits retracted position,

[0039]FIG. 12 is a section A-A of FIG. 11,

[0040]FIG. 13 is a sectional view B-B of FIG. 11, and

[0041]FIG. 14 is a sectional view through FIG. 10 in the region of acircle K of FIG. 10,

[0042]FIG. 15 is a section of a third embodiment of the invention withadvanced cannula, and

[0043]FIG. 16 corresponds to FIG. 15 but for a retracted cannula.

[0044]FIG. 1 shows a cannula system 1 to insert a flexible catheterdesigned as a microdialysis catheter 2 into biological tissue or thelike and comprising a cannula 3 with a sharp front end 4 and a rear end5 against which the cannula 3 is held by a bush-shaped plastic slider 6.Moreover the cannula system 1 comprises a plastic tubular housing 7comprising a front aperture 8 in the region of its front end as seen inthe direction of puncturing and a rear aperture 9 in the region of itsrear end as seen in said direction, the catheter 2 being guided throughsaid rear aperture 9 and being affixed within it to the housing 7. Theslider 6 is held in displacement manner along the cannula's axis in thehousing 7 between an advanced position shown in FIG. 1 wherein the frontend 4 of the cannula 3 axially projects beyond the housing 7 and aretracted position wherein the cannula 3 is received in the housing 7.

[0045] The housing 7 comprises at its top side a slot 17 which is maskedin FIG. 1 but shown in FIG. 2 running in the direction of displacementof the slider 6 and through which passes a radial protrusion 10 of saidslider, a two-arm lever 11 being mounted to that end of said protrusionwhich is away from the slider 6. The lever 11 comprises a front arm 12to which is affixed a detent beak 13 and a manually driven rear arm 14.When the slider 6 is in the advanced position, the detent beak 13resiliently engages from behind the front end, as seen in the directionof puncturing, of the housing 7.

[0046] The catheter 2 is held by a stopper 16 in the rear aperture 9 ofthe housing 7 and runs inside this housing and through the transverseslot 15 into the inside of the cannula 3 as far as almost its front end4.

[0047]FIG. 2 is a topview of the retracted position of the slider 6 ofthe cannula system 1 of FIG. 1. A transverse slot 15 is shown which canbe engaged by the detent beak 13.

[0048]FIG. 3 shows the cannula system of FIGS. 1 and 2, however with theslider 6 retracted and the detent beak 13 engaged in the transverse slot15. In this position the sharp front end 4 of the cannula 3 is withinthe housing 7 and therefore harmless. The catheter 3 projects throughthe front aperture 8 into the housing 7 and thereby is guided in amanner precluding relative motion of catheter 3 and the sharp front end4 of the cannula 3 and also protecting the catheter 3 against damage.

[0049]FIG. 4 is a topview of the configuration of FIG. 3.

[0050]FIG. 5 shows a section V-V of FIG. 1 on an enlarged scale. It isclear that the housing 7 comprises the slot 17 which guides the slider 6together with its radial protrusion 10. The catheter 2 comprises a ductseparation, ie it is a two-duct catheter. However the cannula system 1of the invention also may be used with other catheters.

[0051] The housing 7 comprises a substantially flat surface 18 at itslower side for the purpose of resting against a surface, especially theskin of a human. The front aperture 8 of the housing 7 is oval andcomprises a free inside width larger than the outside diameter of thecannula 3. However the front aperture 8 also may be of such free insidewidth as to substantially match the outside diameter of the cannula 3,whereby the cannula 3 in its retracted position shall be snugly guidedin the front aperture 8. In this manner the catheter 2 is precluded frombeing bent immediately behind the front end 4 of the cannula 3 whenlatter is in its retracted position and being damaged by this end of thecannula 3.

[0052] The drawing however does not show, and therefore discussion ispresently required, that an adhesive strip is mounted on the outside ofthe housing 7 to the flat surface 18, said strip forming a fastener toretain the housing 7 on a surface, in particular the skin of a human.

[0053] The operation of the cannula system 1 of the invention willpresently be discussed in relation to FIGS. 6 through 9 showing variousinsertion stages of the catheter 2 into the tissue of a human using thecannula system 1.

[0054] When inserting the cannula 1 into the patient's skin symbolizedin FIG. 6 by a line 19, the cannula 3 will be in its advanced positionwherein its front end 4 projects axially beyond the housing 7 and beyondthe front end of the catheter 2 and wherein the slider 6 is locked bythe detent beak 13 to the housing 7. To insert the cannula system 1, auser seizes the housing 7, with a finger 20 resting on said housing asshown in FIG. 6, while puncturing the skin 19 with the front end 4 ofthe cannula 3.

[0055] Thereupon the user guides the cannula 3 into the tissue to adesired depth as shown in FIG. 7. Next by his finger 20 he drives therear arm 14 of the lever 11, whereby the detent beak 13 disengages fromthe front end of the housing 7 and the slider 6 together with thecannula 3 thereupon can be displaced in the direction of an arrow 21towards its retracted position.

[0056] In FIG. 8 the slider 6 is in its retracted position wherein thecannula 3 is received in its entirety in the housing 7, thereby reliablypreventing the front end 4 of the cannula 3 from injuring the patient ordamaging the part of the catheter 2 present in the body of the patient.Once the slider 6 is in its retracted position, the user releases thelever 11 which then by its detent beak 13 enters the transverse slot 15of the slot 17 and in this manner locks the slider 6 in its retractedposition to the housing 7.

[0057] Thereupon a protective foil of the adhesive strip mounted on theflat surface 18 may be removed and the housing 7 together with its flatsurface 18 can be deposited flat on the skin 19 as shown in FIG. 9.

[0058] Next, in the position shown in FIG. 9, liquid may be infusedinto, or removed from the tissue by means of the catheter 2.

[0059] Because the cannula system 1 upon insertion of the catheter 2into the tissue remains on said catheter and may not be detached fromit, the handling of the cannula system 1 is substantially simplified andrequires less time.

[0060]FIG. 10 shows a second embodiment of the cannula system. Identicalor corresponding components are denoted by the same references.

[0061] The second embodiment of the cannula system 1 shown in FIG. 10differs from the first embodiment of FIGS. 1 through 9 in that thelocking means to lock the slider 6 on the housing 7 differs in design inthe manner elucidated below in relation to FIG. 14, and in thatdisengaging means are provided which disengage the locking means whenthe cannula 3 is in its advanced position and when the front end of thehousing 7—as seen in the direction of puncturing—arrives in the vicinityof an obstacle such as the skin of a patient.

[0062] In FIG. 10 the slider 6 together with the cannula 3 is in itsadvanced position. The disengagement means comprise a disengagingelement 22 which is displaceably mounted on the housing 7 and of whichthe front end 23 is annular and coaxial with the cannula 3, and of whichthe rear end extends by disengagement blades 24, 25—elucidated furtherbelow in relation to FIG. 13—inside the housing 7.

[0063]FIG. 11 shows the cannula system 1 of FIG. 9 with the slider 6 inits retracted position wherein the cannula 3 is received inside thehousing 7.

[0064]FIG. 12 shows a section A-A in FIG. 11 showing the disengagingblades 24, 25.

[0065]FIG. 13 shows a section B-B in FIG. 11 showing the annular end 23of the disengaging element 22.

[0066]FIG. 14 shows a sectional elevation in the region of a circle K ofFIG. 10.

[0067] The slider 6 is shown in its advanced position in the upper halfof FIG. 14. In this embodiment the slider 6 is fitted with lockingblades which, with respect to the cannula 3, are diametrically opposite,one locking blade 26 being shown in the upper half of FIG. 14 andanother locking blade 26′ being shown in the lower half of FIG. 14. Bymeans of radially inward-pointing protrusions 28, 28′, the lockingblades 26, 26′ resiliently enter radial clearances 29, 29′. The lockingblades 26, 26′ each comprise a bevel 30,30′ at their end facing thedisengaging element 22. A helical spring 31 is mounted between theaxially inner end of the housing 7 and the slider 6 and biases theslider 6 when in its advanced, locked position in the direction oppositethe direction of puncturing, that is in the direction of its retraction.

[0068] The disengaging blades 24, 25 of the disengaging element 22 runthrough apertures 32, 32′ configured radially external to the frontaperture 8 of the housing 7 and they comprise each a bevel 33, 33′ attheir end facing the disengaging blade 26, 26′ which, by said bevel 33,33′ rest against the particular bevel 29, 29′ of the locking blades 26,26′.

[0069] The cannula system 1 of FIGS. 10 through 14 operates as follows:

[0070] For the piercing operation, the slider 6 will be in its advancedposition to insert the cannula 3 so that the locking blades 26, 26′enter by means of their radial protrusions 28, 28′ the radial clearances29, 29′ in the housing 7 and in this manner will lock the slider 6,which is spring-loaded, toward the retracted position against thehousing 7. Illustratively the slider 6 already may be moved into thelocked, advanced position when assembling the cannula system 1. Howevera drive element also may be used in the manner shown in FIGS. 1 through9 to allow manually moving the slider 6.

[0071] As the front end—as seen in the direction of insertion—of thehousing 7 comes into the vicinity of the patient's skin during theinsertion operation of the cannula 3, the annular end 23 of thedisengaging element 22 comes to rest against the skin and upon furtherinsertion of said cannula said end is axially displaced toward thehousing 7, as a result of which the disengaging blades 24, 25 by meansof their bevels 30, 30′ engage from below the bevels 33, 33′ of thelocking blades 26, 27 and lift them and thereby move them out of theradial clearances 29, 29′ in the housing 7, so that the slider 6 is nowdisengaged and, under the bias of the helical spring 31, is returned inthe direction of an arrow 34 into its retracted position.

[0072] Automatic disengagement of the locking means is implemented inthis manner and undesired deep piercing by the cannula 3 is averted andhandling of the cannula system 1 is made easier.

[0073]FIG. 15 shows a third embodiment of the invention. It differs fromthe embodiment of FIGS. 1 through 9 in that the slider 6 isspring-loaded opposite the piercing direction by a spring 34, that istoward the rear of the housing 7. An arm 35 is configured at the slider6 and by its end projects through an aperture 36 into the front part ofthe housing 7, this arm furthermore comprising a hook 37 engaging frombehind a front edge 38 of the housing 7 and in this manner keeping theslider 6 against the loading of the spring 34 in the position shown inFIG. 10. The arm 35 is resilient and accordingly the pressure of thehook may be disengaged from the front edge 38 and as a result the slider6 can be forced to the rear by this spring 34, the slider 6 thencarrying along the cannula 3 affixed to it and both assume the positionshown in FIG. 16.

[0074]FIG. 16 shows that the length of the cannula 3 is such that thesharp front end 4 of the cannula 3 is situated within the front aperture8 of the housing 7, as a result of which the catheter 2 is protectedagainst damage from the sharp front end 4 of the cannula 3 becausekeeping the cannula 3 inside the housing 7 avoids relative motion ofcannula 3 and catheter 2.

[0075] Basically the cannula system of FIGS. 15 and 16 is operated inthe same manner as that of FIGS. 1 through 9 except that the manualreturn of the slider 6 is replaced by the force exerted by the spring34. Disengagement of the hook 37 from the edge 38 is implemented in thatfollowing sufficient insertion of the cannula 3, the projecting hook 37is pressed against the skin surface. Separate actuation of the hook 37is therefore unnecessary.

1. A cannula system, comprising a tubular housing having a front and arear end, a slider displaceable inside the housing between a front limitand a rear limit position, a cannula rigidly joined by its rear end tothe slider and of which the front end fitted with a tip for piercinginto biological tissue or a similar end extends as far as the fronthousing end when the slider is in the rear limit position, a catheterconnected to the housing, and means to move back the cannulacharacterized in that in the direction opposite the direction ofpiercing, the catheter (2) is immovably joined to the rear end of thehousing (7) and/or the slider (6) and at least partly extends throughthe slider (6) and into the cannula (3).
 2. Cannula system as claimed inclaim 1, characterized in that the catheter is rigidly joined to therear housing end and extends up to the front cannula end when the slider(6) is in the front limit position and the cannula (3) projects from thefront end of the housing (7).
 3. Cannula system as claimed in claim 1,characterized by locking means to lock the slider (6) against thehousing (7) at least in the advanced position of the slider (6). 4.Cannula system as claimed in claim 1, characterized by means formanually retracting the cannula (3).
 5. Cannula system as claimed inclaim 4, characterized in that the housing (7) comprises a slot (17)which runs in the direction or displacement of the cannula (3) andthrough which passes a radial protrusion (10) of the slider (6). 6.Cannula system as claimed in claim 4, characterized in that the slider(6) comprises a two-arm lever (11) pivoting about an axis transverse toits direction of displacement and of which the front arm (12), when in adetent position in the front limit position of the slider (6), engagesfrom behind an edge (38) at the front end of the housing (7) and whichcan be disengaged by pressing the rear arm (14).
 7. Cannula system asclaimed in claim 6, characterized in that the slider (6) and the two-armlever (11) are linked to each other by a protrusion (10) projectingthrough a slot (17) in the housing (7) and running in the longitudinaldirection of said housing.
 8. Cannula system as claimed in claim 1,characterized by a spring (34) biasing the slider toward its rear limitposition and by the slider (6) being held in its front limit position bya detent means which can be disengaged from outside the housing (7). 9.Cannula system as claimed in claim 8, characterized in that the detentmeans comprises a hook (25) which is linked to the slider (6) and whichin the front limit position of the slider (6) engages from behind anedge (38) at the front end of the housing (7) and which is resilient inthe direction of disengagement.
 10. Cannula system as claimed in claim9, characterized in that the hook projects beyond the front end of thehousing (7) in such manner that when the cannula (3) is piercing saidhook impacts the tissue surface and disengages the hook (25). 11.Cannula system as claimed in claim 3, characterized in that the lockingmeans comprise a locking blade (26) which is linked with the adapter andwhich in the locking position by means of a radial protrusion (28)resiliently enters a radial clearance (29) inside the housing (7), andin that the disengaging means comprise a disengaging element (22) whichis axially displaceable relative to the housing (7) and of which thefront end projects axially beyond the front end of the housing (7) andthe rear end comprises a disengaging blade (24) which extends into theinside of the housing (7) and upon axial displacement of the disengagingelement (22) engages the underside of the locking blade (26) to move itout of the clearance (29).
 12. Cannula system as claimed in claim 11,characterized in that the disengaging blade (24) and the locking blade(26) when in the rest position rest against each other by means ofbevels (31, 33) in such manner that upon axial displacement of thedisengaging element (22) the disengaging blade (24) lifts the lockingblade (26) toward the housing (7).
 13. Cannula system as claimed inclaim 11, characterized by at least two disengaging blades (24, 25) andby at least two associated locking blades (26, 27) being situatedrelative to the cannula (3) at diametrically opposite sites of thedisengaging element (22) resp. of the slider (6).
 14. Cannula system asclaimed in claim 11, characterized in that the front end (23) of thedisengaging element (22) is substantially annular.
 15. Cannula system asclaimed in claim 8, characterized in that the spring is a helical spring(31) mounted between the housing (7) and the slider (6), in particular acompression spring coaxial with the cannula (3).
 16. Cannula system asclaimed in claim 1, characterized by retention means to keep the housing(7) on a body surface, in particular the skin (19) of a human. 17.Cannula system as claimed in claim 16, characterized in that theretention means comprise adhesives means mounted on the outside of thehousing (7), in particular an adhesive strip.
 18. Cannula system asclaimed in claim 1, characterized in that the housing (7) comprises asubstantially flat surface (18) to come to rest on the body surface, forinstance the skin of a human.
 19. Cannula system as claimed in claim 1,characterized in that the front aperture (8) of the housing (7) is of afree inside width substantially matching the outside diameter of thecannula (3).
 20. Cannula system as claimed in claim 1, characterized inthat the slider (6) comprises a stop for the catheter (2) acting in thedirection of piercing and driving along the catheter when the slider (6)is being advanced.
 21. Application system for catheters fitted with atubular housing fitted with a front and a rear end, said systemcomprising a slider displaceable inside the housing between a front anda rear limit position, a cannula of which the front end comprises a tipfor insertion into biological tissue or the like, said cannula beingreceived inside the housing when the slider is in the rear limitposition and at least partly projecting from the housing when the slideris in the front limit position, a catheter fitted with a front part forinsertion into an object as well as a fluid duct to feed to and evacuatefrom the front part, where upon application of the front catheter part,the cannula encloses the catheter and is received inside the housing.